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684

Compound Pumping Engines.

If!

valve c for the L. P. cylinder is double-ported, but not relieved
from steam pressure at the back. The piston rod YY, being pro-
longed, forms the pump plunger, its sectional area being half that
of the pump piston, for reasons to be explained in the next
chapter. J j is the steam supply pipe to the H. P. cylinder, K its
exhaust, as well as supply for L. P. cylinder, and the L. P. cylinder
exhausts directly into the condenser, as will be seen in Fig, 665.

The surface condenser NN consists of a.rectangular casing, con-
taining a nest of tubes. Cold water being allowed to flow in
through the pipe M, passes through these small tubes, first through
the top half, returning through the lower half, then out by the
pipe L. The exhaust stearn distributing itself outside the tubes,
becomes condensed, is taken away as water by the air pump Q',
and delivered to the hot well u; then by the feed pump v to the
boiler. The air pump bucket has four valves at T, fixed foot